Conventional impact driven sprinkler is mainly consisted of a bearing, an elbow, a nozzle, a swinging arm, and a reversing mechanism. The rotation of the sprinkler is achieved as follows. A water jet sprayed from the elbow impacts on the deflector of the swinging arm which is caused to rotate due to the application of the impact force. The application of the impact force is maintained until the deflector is disengaged with the water jet. The swinging arm, however, continues to rotate and torque is generated on the swinging arm spring. The swinging arm stops rotating when the spring torque reaches a predetermined value. Subsequently, the swinging arm starts to rotate back due to the elastic potential energy of the spring. The elastic potential energy is completely released when the swinging arm rotates back to the water jet. The swinging arm however continues to rotate until it strikes the sprinkler body. A moment of momentum is generated on the latter due to the strike, causing the sprinkler body to rotate by a small angle. The swinging arm then begins a new cycle. During the next cycle, the sprinkler body is stroked to be rotated by a further small angle compared to the position of the sprinkler body in the previous cycle.
In this conventional impact sprinkler, the swinging arm constitutes a key member for achieving rotation. In operation, the swinging arm bears forces including spring force, water impact force, gravity force and strike impact force, with the last one constituting the main reason of fatigue fracture of the swinging arm. The swinging arm is subject to more than 100 times impact during one cycle of rotation. In this way, the strength of the swinging arm has a significant effect not only on the service life and operation reliability of the sprinkler, but also on the reliability and cost of the whole irrigation system.
However, the strength of a member that subject to continuous impact load is particularly dependent on manufacturing process of the member. Currently, the swinging arms used in metal sprinklers are manufactured by casting. Sand holes and blowholes are inevitable during casting, which significantly deteriorate the strength of the well designed swinging arm. The swinging arm thus formed is prone to fatigue fracture after repeated strike.
Another problem existing in this conventional impact sprinkler resides in the fact that the cover range of the sprinkler is affect because a part of the kinetic energy of water stream is consumed by the swinging arm and the swinging arm spring. Further problem existing in this sprinkler is that a number of parts are needed to realize rotation and reversion, causing a high manufacturing cost.